When a cotton fiber carding machine is in operation, the carded fibers on the spikes of the clothing of the main card cylinder are conveyed to the doffer and transferred to it in the form of a fine card web. The doffer, in the same way as the main cylinder, is a cylindrical element which has a spiked clothing on its surface. These spikes on the components may be in the form of teeth or wires.
The exact setting of the doffer relative to the main cylinder is normally fixedly preset in the manufacturer's works. However, there is a range of circumstances in the practical operation of a card when it would be desirable to make the clearance between the spikes of the clothing and the main cylinder adjustable, in order to achieve ideal carding and to ensure an ideal transfer of the carded fibers to the doffer. By this means, the starting operation of a card could be better controlled, temperature dependent elongations could be compensated and adjustments to the staple length could be effected. The problem lies in the fact that this adjustment must be carried out with delicacy as well as friction free and without jerks, without the support of the object tending to oscillate. The achievement of an adjustment of this type is very difficult in practice because of the static friction frequently encountered with mechanical devices. The doffer is namely a relatively heavy structure, so that the adjustment of the latter in an arrangement with very high friction tends to occur with a certain jerk or jolt as soon as the state of rest is converted into a movement to the desired position. This phenomenon is known as so-called stick-slip. In order to overcome this problem one could attempt to support the doffer on rollers, so that the friction is at a minimum. However, the risk then exists that the arrangement easily tends to oscillation.